Manipulate HTML elements added dynamically with 'vanilla' javascript

I'm creating a JavaScript plug-in which needs a fairly large/complex HTML structure to be rendered on the web page, before being manipulated via JavaScript. I don't want to use jQuery at all in this.

I'd like to be able to bundle all of the required code in a single JS file, which can be loaded into a parent web page and it'll 'do its thing'. I'd rather the parent page did not have to include any additional HTML/CSS in order to work - I want everything to come from the single JS resource.

Currently I have the large chunk of HTML in a JavaScript variable as a string: